As one of the widely used atmospheric particle samplers an impactor is used for measurement of aerosol size distribution and collection of samples for further chemical analysis. Though it has been used widely, there are still problems to be overcome. When the suspended particles are liquid, its actual collection efficiency is very close to the theoretical collection efficiency. However, when it is used in the collection of solid particles, the collection efficiency is much lower than the theoretical efficiency because solid particles will rebound from the impaction plate, and the rebounded particles can be easily carried away by the aerosol stream if the conventional fiat impaction plate is used.
There are ways to reduce particle rebounding from the impaction plate, such as application of grease on the surface of the impaction plate. However, two essential questions exist in this method: firstly the chemical properties of the grease itself will interfere with chemical analysis of the collected particles; and secondly the incoming particles will rebound from the particles that have been adhered to the impaction plate. Consequently the collection efficiency is lowered.
Blowing away of the particles from the impaction plate is another problem of the conventional impactor. When the particles have been accumulated to a certain thickness on the plate, the particles will be blown away by the air stream, causing another loss of particles.